Well it isn't a good deal unless it is under $400.
You are joking right? $800 is the going rate for a mint Stargate.
In real the real world the prices on the Williams games started dropping like a rock once the Multi-Williams came out. I was at an auction last year that had every Williams game other than Mystic Marathon in attendance, and the only one that went over $400 was a mint Sinistar that was very early in the auction.
Checking ebay there is only one complete Stargate in reviewable history that actually sold. It was a caberet that worked all the way and it sold for $307.